I would argue that the definition of SEO might not be something that everyone understands/defines in the same way. If you're thinking about this community then I think you're right in thinking that SEO has a pretty universal meaning. But, if you're talking to people outside the SEO community then you're going to get some pretty broad definitions that will often include reference to paid search. I personally like the term inbound marketing for SEO and related work, but it really comes down to who you're talking to and what you're trying to convey.